Spark-ignition internal combustion engines include an ignition apparatus comprised of, for example, an ignition coil that causes a spark plug to generate a discharge, so that the generated discharge causes fuel introduced in the combustion chamber of the internal combustion engine to be burned.
Proposed multiple-discharge ignition apparatuses are configured to cause the spark plug to generate plural discharges during one combustion cycle in order to improve the combustion state of fuel.
Patent document 1 discloses an example of these multiple-discharge ignition apparatuses. The ignition apparatus uses, as an ignition coil for causing a spark plug to generate discharges, an ignition coil including in combination a primary coil coupled to a storage coil, and a secondary coil coupled to the spark plug.
Specifically, the ignition apparatus repeatedly performs a task that turns on a first switch connected in series to the storage coil to charge the storage coil, and turns off the first switch to cause the storage coil to discharge.
The ignition apparatus also repeatedly performs a task that
(1) Turns on a second switch connected in series to the primary coil to charge the primary coil during the discharging from the storage coil, i.e. the turn-off of the first switch, thus causing a current with a predetermined direction to flow through the spark plug via the secondary coil
(2) Turns off the second switch to cause the primary coil to discharge during the charging of the storage coil, i.e. the turn-on of the first switch, thus causing a current with a direction opposite to the predetermined direction to flow through the spark plug via the secondary coil.
Specifically, the ignition apparatus alternately turns on the first switch and the second switch to cause currents respectively having different directions to alternately flow through the spark plug. This results in multiple discharges, i.e. alternating-current discharges, via the spark plug.
For example, patent document 2 discloses such a multiple-discharge ignition apparatus.